The invention pertains to vertical cavity surface emitting lasers (VCSEL's), and particularly to VCSEL's having a constant output. More particularly, the invention pertains to VCSEL's having power output monitors and feedback power control mechanisms.
Electrical parameters of lasers may vary due to effects such as manufacturing tolerance, temperature and aging. Control of power output and bias conditions enhances performance of semiconductor lasers. Control of output power also allows relaxation of parameters, thus increasing the yield of useful devices. In fiber optic applications, the desired power output is the highest value consistent with eye safety and long term reliability. It is common practice to monitor the output power of the laser and feedback a portion of the signal to circuitry which controls the operating conditions of the device. A critical requirement is that the ratio of the feedback signal to the coupled power output be constant. The problem in maintaining a relationship between the feedback and output is linearity for maintaining constant proportional output under varying conditions of the VCSEL.